1. Field of the Invention
The present invention generally relates to an improvement for engine fuel delivery systems. More specifically, the present invention relates to an engine fuel delivery system that is especially useful in automobile engines that employ compression ignition and direct fuel injection, such as diesel engines.
2. Background Information
One example of a diesel engine technology for achieving low fuel consumption and low emissions is disclosed in Japanese Laid-Open Patent Publication No. 7-167003. This publication discloses a practical diesel engine that uses an accumulator vessel called a “common rail.” This technology, the engine is provided with a plurality of fuel injection valves for each cylinder of the engine, a high-pressure fuel pump rotatably driven using the engine output as a power source, and a common rail provided in the high-pressure line that fluidly connects the fuel injection valves and the high-pressure pump together. Since the fuel is maintained at a high pressure inside the common rail, stable high-pressure fuel injection can be accomplished at all times and the combustion efficiency can be improved through atomization of the fuel spray.
When the high-pressure fuel pump is driven by the engine at a fixed ratio of the engine rotational speed, the pressure generated inside the common rail by the high-pressure pump increases substantially proportionally to the engine rotational speed. Thus, during the initial stage of engine starting when the engine rotational speed is low, it is difficult to sufficiently increase the fuel pressure inside the common rail. Consequently, during the initial stage of engine starting, the atomization of the fuel spray resulting from high fuel pressure, which is the essential benefit of using a common rail, cannot be achieved. More particularly, in the case of cold starting, the period of unstable combustion is long, presenting the possibility of degraded fuel consumption and increased emissions of HC, NOx, and smoke.
Japanese Laid-Open Patent Publication No. 10-9074 discloses a technology for a direct fuel injection gasoline engine in which a variable speed device is inserted in the power transmission path between a camshaft driven by the engine and the high-pressure fuel pump. During the period from starting of the engine using the starter key until complete explosion of the engine, i.e., during cranking of the engine when the starter motor is substantially driving the engine, the fuel pressure is increased for a short period beginning from engine starting by increasing the speed of the variable speed device.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved engine fuel delivery system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.